This invention relates to flame-resistant, rigid foam compositions which are produced from foamable, modified polyurethane resins.
Rigid foams of the polyurethane type have a wide variety of industrial and commercial applications. For example, because of extreme buoyancy, rigid polyurethane foam is used as a flotation material in such items as boats, floating docks, surf boards and water closet ball floats. Because of the ability to assume shapes necessary to fill non-uniform voids, rigid foam finds application as a packaging material. In the aircraft industry, rigid foams are employed as structural reinforcement elements in wingtips, flaps, ailerons, and so forth. Such applications employ the foams as rigidizing agents which bond-in-place to metal or fiber glass skins to provide continuous skin support, thus eliminating rib-type construction.
The primary use of polyurethane-type rigid foams, however, is as an insulating material. As an insulator, rigid foam may be applied to walls, floors, roofs and the like as a preformed slab of varying thickness. It may be applied as a molded slab to such contour shapes as pipes and conduits, or it may be foamed in place to fill small openings and crevices, or to fill the air space between an outer and an inner construction surface. Polyurethane-type rigid foams possess many advantages as insulating materials. They provide the highest efficiency of any presently available insulation resulting in the lowest weight and volume for a given application. These foams possess excellent water, solvent and chemical resistance, are easily applied, can be mold formed and have good adhesive qualities.
Foamable polyurethane resin compositions may be described basically as the reaction products of polyisocyanates and polyhydric alcohols. Foam resin compositions are prepared from the components simply by mixing the polyol and the polyisocyanate. The addition of water or a low boiling fluorocarbon as a blowing agent is a common expedient to obtain better foaming action. Other components such as siloxane glycol surfactants which improve cell configuration, or catalysts such as tertiary amines, tin alkyls or the tin salts of organic acids, may be added to the reaction mixture prior to foaming. Addition of heat or pressure is necessary to achieve foaming for the so-called "hot foam" compositions, but "cold foam" compositions may be conveniently foamed at ambient temperature pressure.
Foam compositions prepared according to the manner described frequently do not provide the degree of fire retardance and self-extinguishment which is required of a particular insulating or building material. To achieve foams which have satisfactory properties of this nature, it is often necessary to add a flame retarding agent to the foam compositions. Such agents may be, for example, inert solids such as antimony trioxide or liquids such as halogenated organo-phosphorous derivatives. While the use of such fire retardants has, in general, advantageous effects on the fire-resistant properties of a foam composition, it is not a completely satisfactory method of increasing fire resistance. For example, such agents increase the storage and handling problems connected with foamed resin compositions. Another disadvantage of these agents is that they may result in a foam composition which has non-uniform fire-resistant properties because of uneven distribution of the agents throughout the foam. An additional disadvantage of some of the more sophisticated fire-retardant agents is, of course, cost.
Recently, however, various improvements have been discovered which modify polyurethane compositions by incorporating in the molecular structure of the foams additional components. These components, which frequently contain halogens tend to give foam of improved fire-resistance. One example of such improvements is disclosed in Belgian Pat. No. 674,252 in which trimellitic anhydride is chemically incorporated in the foam. Another example, disclosed in Ser. No. 723,593 filed Apr. 23, 1968 by S. H. Marcus, comprises certain novel adducts of polyhydric alcohols and polyfunctional carboxylic acid anhydrides which are used instead of a conventional polyol in foam formation.
I have now discovered that substituting the monomeric imide product of the pre-reaction of a polyarylpolyisocyanate and a polyfunctional carboxylic acid anhydride for the isocyanate component in a urethane-type foam produces foamed products having excellent fire-resistant properties. This monomeric imide product was disclosed and patented by me in U.S. Pat. No. 3,823,158. As can be seen in Table II all the foams containing the monomeric imide component had retained their weight in excess of 80 percent while the samples without the incorporation of the imide only 53 to 60 percent of the weight was retained. Foam compositions prepared according to my invention also give improvements over modified urethane foams such as those discussed above.